The present invention relates to an apparatus and a method for the detection of the level of the different phases present in at least one tube or vessel the content of which is intended for filling the different wells of a microplate-format container for an automated analysis system. According to the invention, this detection is carried out by reflecting light on a point zone on the outside of the tube, during a displacement of the tube along an optical reader or the optical reader along the tube in a rectilinear movement and in a known manner.
It relates moreover to such an apparatus or method operating by illumination with monochromatic light and detection of the amount of reflected light, with the phase differences being recognized by the sudden variation in the amount of reflected light.
Increasingly, many methods in laboratory chemistry are automated, for example chemical analyses or DNA sequencing. The different products to be mixed together are handled by robotic equipment, and the entire procedure is controlled and monitored by computer. The rapid growth of large-scale DNA analyses, for example by PCR-type methods, has increased the requirements in this field and makes even the smallest improvement in the productivity and reliability of these procedures and the corresponding equipment worthwhile.
Within the technical capabilities of each facility, an effort is made, as far as possible, to carry out the procedure while minimizing the manual operations that give rise to loss of time and the risk of error.
Typically, an integrated automated facility is used that includes computerized monitoring of the products and samples processed. Such a facility comprises one or more robot operating heads, for example a pipetting instrument which takes an accurate shot of a liquid from a vessel in order to transfer it to another vessel, where a reaction will then take place. This vessel can then be moved to another slot for another operation, and/or stored in a waiting slot during the reaction, possibly in a reactor ensuring specific conditions of temperature, pressure, humidity, etc.
For reasons of reliability of analysis and productivity, receptacles of a standardized so-called “microplate” type are most usually used. Such a receptacle usually comprises a monolithic surface area pierced by a large number of wells of a few millimeters in diameter which are independent of each other. Other types of microplates also exist which are here included under the same name, for example a tray or rack comprising positions in which the same number of moveable individual tubes are inserted, and performing a function similar to the wells of a monolithic plate. Depending on the versions, a single plate can contain for example 96 or 384 wells. Several wells of a single microplate are often processed in parallel by multi-head pipetting instruments, which can be controlled together or separately.
These plates all have a single external geometry, in particular in their base footprint. This geometry is governed by a standard called “SBS” (ANSI/SBS 1-2004), which allows compatibility of all the plates with the majority of the robots and specialized machines in this field. This geometry comprises for example a rectangular base having two cut off chamfered angles, and is equipped with a rim having a slight horizontal extension around the base. This standardized shape allows all the compatible robots to use a robot arm equipped with a compatible slot for receiving, gripping and holding all the plates in a firm, precise and repeatable manner.
In some circumstances, and in particular for most analyses of blood or biological fluids, the automated analysis or processing comprises a separation phase, for example by centrifugation or decantation, which makes it possible to separate the different constituents present within the fluid initially taken.
For example in the case of blood, the initial sample is poured into a test tube, also called a sample tube, which is then centrifuged. The result of this centrifugation gives a distribution of the different constituents on several different levels, forming the following phases:                at the bottom of the tube is found a thick, dark red phase containing the red blood cells;        above this is found a thin, whitish phase forming a sort of emulsion called “buffy coat”, which mainly contains white blood cells;        at the top is found a lighter red fluid phase formed by the plasma, which represents approximately 55% of the blood volume.        
In order to use a single one of the constituents separated in this way, a pipetting instrument is used that is made to descend in the tube until reaching the depth where the constituent in question is found, for example into the buffy coat for sampling white blood cells. The component thus sampled is then poured into one or more receptacles, for example for a series of wells within a microplate, an operation which is often called “filling” the microplate.
In the centrifugated tube, the vertical position of the different phases varies according to many parameters, such as the initial amount of fluid or the diameter of the tube. In order to make it possible to automate sampling in a particular phase, it is therefore necessary for the robot to be provided with an apparatus for the detection of the levels of the different phases in each of the tubes to be sampled.
Different types of apparatus are known for carrying out this detection. Certain equipment measures for example the variation in the light transmitted by the content of the tube. These methods have drawbacks owing for example to the variability of the transmission factors. Furthermore, the transmission does not make it possible to distinguish between opaque phases even if they contain different constituents. Other methods measure fluorescence emitted by the content of the tube under chemiluminescence, but require relatively complex, costly high-power instruments for this purpose.
U.S. Pat. No. 4,683,579 proposes to measure the scattering of incident light of 400 to 1000 manometers at a narrow angle of the order of 20°. The precision of this technique however can be insufficient, and represents a significant space requirement around the tube which is inconvenient for incorporation in a robot system.
U.S. Pat. No. 7,450,224 proposes to carry out computerized graphical analysis of a complete colour image of the tube. For this purpose, the tube is gripped by a robot gripper and brought into an imaging chamber containing a CCD multipixel colour camera and uniform multidirectional lighting. The tube is extracted from a rack positioned on a table with XY displacement.
This technique however has drawbacks, for example requiring relatively costly components and complex computer processing requiring a certain computing power. Furthermore, such an apparatus permanently occupies a certain space and requires a table with robotized displacement in order to make an automated choice of the tube to be sampled.